The average number of weighings to locate a counterfeit coin (Corresp.)

A solution is obtained to the problem of finding the minimum of the average number of weighings, using a balance, needed to locate one light coin from among
n
coins of which
n - 1
are genuine and of the same weight. Optimal strategies are determined, and the anomaly that it may be better to work with
n + 1
coins rather than
n
is examined and explained.